Feedthrough apparatus with noble metal-coated leads

ABSTRACT

Methods and apparatuses are provided for an electrical device that employs a feedthrough including a hermetic seal that seals an interior region of the electrical device. The electrical device includes an electrical contact disposed within the interior region of the electrical device, and a wire terminal that includes an encircled portion that is encircled by the feedthrough, and a first end that electrically connects with said electrical contact. When the electrical device is constructed, the first end of the wire terminal is coated with a conductive metal that is more resistant to oxidation than the wire terminal. The first end of the wire terminal is secured to the electrical contact using a mechanical device such as a crimping connector or a spring connector.

FIELD OF THE INVENTION

The present invention relates to electrical devices that incorporateelectrical feedthroughs, and to their method of fabrication. Moreparticularly, the present invention retates to improving theconductivity of metal leads that are part of electrical feedthroughs,and also improving their connectivity with conductive contacts.

BACKGROUND OF THE INVENTION

Electrical feedthroughs serve the purpose of providing a conductive pathextending between the interior of a hermetically sealed container and apoint outside the container. The conductive path through the feedthroughcomprises a conductor pin or terminal that is electrically insulatedfrom the container. Many such feedthroughs are known in the art thatprovide the conductive path and seal the electrical container from itsambient environment. Such feedthroughs typically include a ferrule, andan insulative material such as a hermetic glass or ceramic seal thatpositions and insulates the pin within the ferrule. Electrical devicessuch as biorhythm sensors, pressure sensors, and implantable medicaldevices (IMD's) such as pulse generators and batteries often incorporatesuch feedthroughs. Sometimes it is necessary for an electrical device toinclude a capacitor within the ferrule and around the terminal, thusshunting any electromagnetic interference (EMI) at high frequencies atthe entrance to the electrical device to which the feedthrough device isattached. Typically, the capacitor electrically contacts the pin leadand the ferrule.

Some of the more popular materials that are used as a feedthroughterminal are susceptible to oxide growth, which can act as an insulatorinstead of a conductor over the surface of the pin lead, particularly ifthe oxide growth is extensive. For instance, during fabrication of afeedthrough/capacitor combination the central terminal is subjected toone or more heat treatments. Even though feedthroughs are typicallymanufactured in an inert atmosphere, high temperatures will encourageoxidation if there is residual oxygen from a sealing gas or fromdissociation of surface adsorbed water on fixtures and components.Oxidation of the terminal affects the conductivity of the pin lead andits ability to make good electrical connections with other elements. Theability for the surface oxidized pin terminal to be electricallyconnected to a contact would be particularly impaired if mechanicalmeans such as crimping were employed to establish an electricalconnection. This impairment is troublesome in cases where mechanicalmeans might be less time consuming or less costly than other joiningmethods such as welding.

Accordingly, it is desirable to provide a method of manufacturing anelectrical apparatus incorporating a feedthrough device whereinmechanical means are employed to establish an electrical connectionbetween the feedthrough leads and a contact of the electrical apparatus.In addition, it is desirable to provide a feedthrough device that can beutilized in such a method. Furthermore, other desirable features andcharacteristics of the present invention will become apparent from thesubsequent detailed description and the appended claims, taken inconjunction with the accompanying drawings and the foregoing technicalfield and background.

SUMMARY OF THE INVENTION

A medical device is provided that is efficiently manufactured. Themedical device comprises an encasement, an electrical device disposedwithin the encasement, an electrical contact coupled to the electricaldevice, and a feedthrough assembly. The feedthrough assembly comprises aferrule extending through the encasement and having an inner surface, aterminal extending through the ferrule and having a first end extendinginto the encasement, a conductive metal coating that is more resistantto oxidation than the terminal covering the first end of the terminal,and a body of insulation material disposed between the terminal and theinner wall for preventing the ferrule from electrically contacting theterminal. The medical device also comprises a connector for electricallycoupling the first end to the electrical contact.

A feedthrough assembly is also provided that includes the feedthroughdescribed above, and a connector that is connected to a first end of thefeedthrough assembly terminal for electrically coupling the first end ofthe terminal to an electrical contact.

Also, a method of manufacturing a medical device is provided. The methodcomprises the steps of deploying an electrical device within anencasement, the electrical device being coupled to an electricalcontact, and forming the above-described feedthrough assembly in theencasement. Then, the first end of the feedthrough assembly terminal iselectrically coupled to the electrical contact using a connector.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and

FIG. 1 is a sectional view of an electrical feedthrough thathermetically seals and electrically connects with a contact by way of aconductive metal-coated terminal, where the electrical connection ismade using a mechanical joining device, according to an embodiment ofthe present invention;

FIG. 2 is a sectional view of an electrical feedthrough thathermetically seals and electrically connects with a contact by way of apartially conductive metal-coated terminal, where the electricalconnection is made using a mechanical joining device, according to anembodiment of the present invention;

FIG. 3 is a sectional view of an electrical feedthrough thatincorporates a capacitor and hermetically seals and electricallyconnects with a contact by way of a conductive metal-coated terminal,where the electrical connection is made using a mechanical joiningdevice according to an embodiment of the present invention;

FIG. 4 is a cross sectional view of a crimping apparatus electricallycoupling a noble metal-coated terminal to an electrical contactaccording to an embodiment of the invention.

FIG. 5 is a cross sectional view of a spring connection electricallycoupling a noble metal-coated terminal to an electrical contactaccording to one embodiment of the invention.

FIG. 6 is a cross sectional view of an electrical feedthrough thathermetically seals and electrically connects with a first contact by wayof a conductive metal-coated terminal, and with a second contact by wayof a conductive metal-coated ferrule, where both electrical connectionsare made using mechanical joining devices according to an embodiment ofthe present invention; and

FIG. 7 is an isometric view of a medical device incorporating theelectrical feedthrough illustrated in FIG. 6.

DETAILED DESCRIPTION OF THE DRAWINGS

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, brief summary or the following detailed description.

Referring now to FIG. 1, there is depicted one embodiment of anelectrical feedthrough 100 which is intended for use in conjunction withan electrical device, an exterior container 40 of the electrical devicebeing in contact with the feedthrough 100. The term “electrical device”used hereafter refers to any device incorporating an electricalfeedthrough, including but not limited to biorhythm sensors, pressuresensors, and various IMD's such as pulse generators and batteries.Although the discussion of the feedthrough device throughout thespecification is directed to devices employing glass-to-metal,ceramic-to-metal, or ceramic-to-metal polymer type seals, it is to beunderstood that the principles of the invention are of generalapplication to any feedthrough utilizing a pin lead for the purpose ofmaking electrical connection to any contained electrical device which isto be sealed from its ambient environment. The principles of theinvention are also applicable to multiple pin feedthroughs.

The feedthrough 100 of the present invention includes a center pinterminal 12, with a portion of the length of the terminal 12 passingthrough a ferrule 10. Electrical feedthroughs that are used in IMD's andother biological devices may inadvertently come into contact with bodyfluids. Thus, it is desirable that the terminal 12 be made of abio-stable material. For example, the terminal 12 may consist of orinclude niobium, titanium, tantalum, and alloys of the metals, and otherbio-stable conductive metals. Preferably, the terminal 12 ismanufactured using a refractory metal. In a typical installation, oneend of the terminal 12 extends through a capsule or container 40 intothe interior 15 of the electrical device, and electrically connects withat least one internal contact 34. Another end of the terminal 12 extendsto the exterior 25 of the electrical device.

The insulating material 14 surrounds a portion of the length of theterminal 12. In an exemplary embodiment of the invention, the insulatingmaterial 14 includes glass or glass-ceramic joined directly to conductormaterials by heating or a ceramic joined to conductor materials by brazematerial by heating, or high dielectric polymers such as polyimides. Ifthe insulating material is a ceramic material, the material ispreferably ruby, sapphire or polycrystalline alumina. The composition ofthe insulating material 14 should be carefully selected to have thermalexpansion characteristics that are compatible with the terminal 12. Theinsulating material 14 prevents a short circuit between the terminal 12and the ferrule 10 or the container 40.

In order to ensure a tight seal between the glass 14 and the walls ofthe container 40, the ferrule 10 is disposed as a thin sleevetherebetween. Typically the ferrule 10 has an annular configuration, butmay have any configuration suitable for use with the container for theelectrical device. The ferrule 10 may be formed of titanium, niobium,tantalum, zirconium, any combination thereof, or any other suitablemetal or combination of metals. The ferrule 10 is affixed to the innersurface of the container 40, preferably by welding although any othersuitable means, such as gluing or soldering, may be used.

In order to prevent oxide formation on the terminal 12 and the contactresistance instability attributed to such oxide formation, the terminal12 is coated with a thin film 30 of a conductive metal that is lesseasily oxidized than the terminal 12. Preferably, the conductive metalfilm 30 comprises a noble metal or an alloy of noble metals. The noblemetals include gold, platinum, palladium, rhodium, ruthenium, andiridium. These metals and alloys thereof are highly resistant tooxidation, and consequently protect the terminal 12 from hot, humid, oreven liquid environments. The protection provided by the noble metalsand alloys thereof decrease the contact resistance, and thereforeincrease the stability of crimp connections between a contact and theterminal 12. The conductive metal film 30, hereinafter referred to asthe noble metal film 30, is applied by DC magnetron sputtering or RFsputtering in an exemplary embodiment of the invention, although otherconventional techniques may be used such as chemical vapor deposition,cladding, vacuum depositing, painting, other types of sputtering, etc.The noble metal film 30 is deposited at a minimum thickness of about 100Å, and preferably is at a thickness ranging from about 3000 Å to about7000 Å.

In an exemplary embodiment of the invention, an intermediate film 13 maybe deposited on the terminal 12 prior to deposition of the noble metalfilm 30. The thin intermediate film 13 is a refractory metal, preferablytitanium or niobium, and enhances the adhesion of subsequent metaldepositions to the terminal 12. The intermediate film 13 is applied byany conventional technique such as sputtering, chemical vapordeposition, vacuum depositing, painting, or cladding, and is preferablyapplied using either DC magnetron sputtering or RF sputtering.

According to the embodiment of the invention depicted in FIG. 1, thenoble metal film 30 coats the regions of the terminal 12 that are bothwithin and outside the feedthrough device 100 in a continuous manner.The manufacturing process for this embodiment includes the step ofcoating the terminal 12 with the noble metal film 30 using anappropriate technique prior to forming the hermetic seal between theinsulating material 14 and the terminal 12. When the insulating material14 is a body of glass, the feedthrough seal is formed by applying moltenglass between the terminal 12 and the ferrule 10, and allowing themolten glass to solidify. This process is generally referred to as“glassing” in the art. A ceramic material can also be included asinsulation material, either in place of or together with a glassmaterial.

The noble metal should be carefully selected to ensure that the noblemetal film 30 does not disrupt the stability of the hermetic seal thatwould be formed between the insulating material 14 and the terminal 12in the absence of the noble metal film 30. If the entire terminal 12 iscoated with the noble metal 30 prior to forming the seal, then the noblemetal 30 must be of the type which can readily react with or diffuseinto the metal that forms the terminal 12. As a result of properreactivity and diffusion between the two metals, the insulation material14 will be able to wet and react with the material forming the terminal12, and not only with the noble metal film 30. Following formation ofthe seal between the insulating material 14 and the terminal 12extending therethrough, the ferrule 10 is affixed to the inner surfaceof the container for the electrical device using any conventionalmethod, and preferably using a welding technique.

An electrical connection between the terminal 12 and the contact 34 issecured by a crimping device according to one embodiment of theinvention. Turning now to FIG. 4, a cross sectional view of a crimpingdevice 32 is depicted, the crimping device 32 placing a mechanical forceon both the terminal 12 coated with the noble metal film 30, and thecontact 34. Many known crimping devices can be used in place of thesimple crimping mechanism 32 depicted in FIG. 4. Because the terminal 12is protected from oxidation due to the presence of the noble metal film30, low resistance crimp connections between the terminal 12 andconventional contacts such as copper wires or cables may be provided inplace of more complicated types of connections. Crimping connections aremuch less expensive than connections involving alloying or heat joiningsuch as welding. Also, crimping is among the easiest and the leastexpensive of mechanical methods for joining terminals with other wiresor cables. Consequently, the method of the present invention forcrimping a noble metal film-coated terminal is a highly advantageous andcost saving option for designing electrical devices that employfeedthroughs to hermetically seal the interior components of theelectrical devices.

According to another embodiment, the electrical connection between theterminal 12 and the contact 34 is secured by a spring connection. FIG. 5depicts a cross sectional view of a spring device 36, the spring device36 placing a mechanical force on the terminal 12 coated with the noblemetal film 30, and electrically coupling the terminal 12 with thecontact 34. The spring device 36 shown in FIG. 5 is just one of manyknown spring devices that can be used according to the presentinvention.

Another embodiment of the invention is depicted in FIG. 2. Many of thefeatures depicted in FIG. 2 are identical to those discussed above.Also, the connection between the terminal 12 and the contact 34 using acrimping device 34, a spring contact 34, or other surface contact isapplicable to all embodiments of the present invention, even if notdepicted in all of the drawings.

In the embodiment depicted in FIG. 2, the terminal 12 is not coated witha noble metal film 30 throughout the interior portion of the feedthroughdevice 200. The electrical device is manufactured by first inserting theterminal 12 into the feedthrough device 200, with the noble metal film30 being either absent altogether, or absent from at least the regionsof the terminal 12 that will be reacted with the insulating material 14to form a hermetic seal. A sealing technique as described above is thenperformed to seal the insulation material 14 to the other feedthroughassembly components. Because of the absence of the noble metal film 30in the seal region of the feedthrough 200, consideration need not begiven for potential disruption of the stability of the hermetic sealthat is to be formed between the insulating material 14 and the terminal12. The exposed terminal 12 exterior to the feedthrough 200 is coatedwith the noble metal 30 after seal manufacture and consequently thenoble metal 30 need not be of the type which can readily react with ordiffuse into the metal that forms the terminal 12, although suchproperties may still be advantageous for other reasons. Followingformation of the seal between the insulating material 14 and theterminal 12 extending therethrough, the ferrule 10 is affixed to theinner surface of the container for the electrical device using anyconventional method, and preferably using a welding technique.

As mentioned above and depicted in FIG. 2, the noble metal film 30 isselectively deposited onto the terminal 12 in order to avoid having thenoble metal in contact with the insulating material 14 during glassingor any other suitable sealing method. One way that the noble metal film30 can be selectively deposited is by employing a method wherein theterminal 12 is masked with a masking material before the noble metalfilm 30 is formed thereon. The mask can be applied to the terminal 12using chemical or mechanical masking techniques. The noble metal film 30is then formed outside of the areas that will be critical sealingregions, and at least over the region of the terminal 12 that is to becrimped to the contact 34. The masking material is then removed. Theselectively coated terminal is then inserted into the feedthrough 200and the seal manufacturing method is performed.

Another way that the noble metal film 30 can be selectively deposited isby performing the seal manufacturing method with a terminal 12 that iscompletely free of any noble metal film. Then, the insulative pathbetween the terminal 12 and the ferrule 10 or other metal serving as aconductor is isolated using chemical or mechanical masking methods.After isolating the conductors from one another, the noble metal film 30is applied at least over the region of the terminal 12 that is to becrimped to the contact 34.

The embodiment of the invention depicted in FIG. 3 is similar to that ofFIG. 2 in that the terminal 12 is not coated with a noble metal coating30 throughout the interior portion of the feedthrough device 300. Themethod discussed above can be applied to an electrolytic capacitorfeedthrough for providing a noble metal film 30 as a partial coating onthe terminal 12 of the feedthrough 300. The feedthrough 300 includes acapacitor within the feedthrough ferrule 10. The capacitive structuremay include a multi-layer ceramic structure of annular discoidal shapehaving several sets of thin, spaced apart, electrically conductiveelectrode plates 20 that are separated by thin layers of ceramicdielectric insulating material 22. The capacitor also includes first andsecond mutually isolated electrically conductive exterior and interiortermination surfaces 24 and 26 and insulative end surfaces 28. Thealternative methods for selectively coating the noble metal film 30 overthe terminal 12 are employed in the same manner that they are employedin the embodiment depicted in FIG. 2.

Tests performed on the electrical device incorporating the feedthroughapparatus depicted in FIG. 1 revealed that the noble metal coating doesnot detrimentally affect the hermeticity of the seal provided by thefeedthrough apparatus. Several examples of the configuration of thepresent invention were tested by first sputter coating approximately7000 Å of gold, platinum, palladium, ruthenium and rhodium ontorespective tantalum wire leads prior to hermetic seal manufacture. Theleads were then subjected to a hermetic sealing process that includedglassing insulative material onto the noble metal-coated terminals. Theterminals were then crimped to standard gold plated copper-berylliumcontacts and subjected to standard environmental testing. The testinginvolved exposing the crimped terminals and contacts to temperatures of85° F. and 85% relative humidity for long periods of time. All wireswere 0.011″ In diameter.

Contact resistance was measure before and after testing. Table 1 belowis a summary of the test results.

TABLE 1 Au Pt Pd Ru Rh Resistance Ta Pt Coated Coated Coated CoatedCoated (mhoms) Wire Wire Ta Wire Ta Wire Ta Wire Ta Wire Ta Wire Intl.Ave. 146 7.52 23.8 10.73 9.4 10.16 10.87 Std. Dev. 93.2 0.19 9.03 0.640.69 0.86 0.85 Shift Ave. 104.3 40.6 59.1 49.17 0.78 −0.21 2.17 (posttest) Std. Dev. 144.6 0.37 54.2 101.5 1.5 3.21 1.85

The test results that are summarized in Table 1 show that significantimprovements in both initial contact resistance and resistance shiftresulted from coating tantalum wires with various noble metals, whencompared with a contact involving bare tantalum wire. The improvementswere especially significant when the noble metal film was a palladium,ruthenium, or rhodium coating. Similar improvements result from any ofthe noble metals as coatings of other refractory metal terminals.

Turning now to FIGS. 6 and 7, another embodiment of the feedthroughassembly with metal coated leads according to the present invention isillustrated in the environment of a pacing device 400, although the usefor the illustrated feedthrough assembly is in no way limited to such adevice. Many of the features depicted in FIGS. 6 and 7 are identical tothose discussed above. In FIGS. 6 and 7, the feedthrough terminal 12coated with the noble metal film 30 and is securely engaged with aspring contact 36. The spring contact 36 is welded or otherwise joinedto a conductive socket housing 42 which laterally surrounds the springcontact 36. The socket housing 42 is welded or otherwise secured to aflex circuit 46 which includes circuitry laminated within an insulativematerial. The spring contact 36 and the socket housing 42 couple theterminal 12 with selected circuitry within the flex circuit 46.

The ferrule 10 is also coated with a conductive metal film 48 accordingto this embodiment. The film 48 enables an electrical contact to beelectrically coupled to, and mechanically engaged with, the ferrule 10using a surface contact including but not limited to the crimpingconnection or the spring contact discussed above. The construction shownin FIGS. 6 and 7 includes a spring contact 44 that securely engages withthe film 48 and electrically couples the ferrule 10 with selectedcircuitry within the flex circuit 46. The conductive metal film 48 canbe formed from any metal that is less easily oxidized than the ferrule10, but is preferably a noble metal or an alloy of noble metals.

Suitable noble metals include gold, platinum, palladium, rhodium,ruthenium, and iridium, although titanium, niobium and alloys oftitanium or niobium are preferred. Just like the metals used for thefilm 30 that coats the feedthrough terminal 12, these metals and alloysthereof protect the ferrule from hot, humid, or liquid environments. Theprotection provided by the noble metals and alloys thereof decrease thecontact resistance, and therefore increase the stability of surfaceconnections between a contact and the ferrule 10. The film 48 is appliedby DC magnetron sputtering or RF sputtering in an exemplary embodimentof the invention, although other conventional techniques may be usedsuch as chemical vapor deposition, cladding, vacuum depositing,painting, other types of sputtering, etc. The film 48 is deposited at aminimum thickness of about 100 Å, and preferably is at a thicknessranging from about 3000 Å to about 7000 Å.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing the exemplary embodiment or exemplary embodiments. Itshould be understood that various changes can be made in the functionand arrangement of elements without departing from the scope of theinvention as set forth in the appended claims and the legal equivalentsthereof.

1-64. (canceled)
 65. An implantable medical device for delivering atherapy, the device comprising: a hermetically-sealed containerenclosing an electrical device; a feedthrough coupled to the container,the feedthrough comprising: a generally annular ferrule adapted to matewith an opening in the container; insulating material disposed withinand coupled to the ferrule; and a terminal conductor extending throughand sealed to the insulating material and having a proximal portiondisposed outside of the container and a distal portion disposed withinthe container, the terminal conductor comprising an inner core and anoxide-resistant cladding on the inner core; and a connection between thedistal portion of the terminal conductor and the electrical deviceenclosed in the container.
 66. A medical device according to claim 65,wherein the oxide resistant cladding comprises a noble metal or a noblemetal alloy.
 67. A medical device according to claim 65, wherein theoxide resistant cladding comprises a conductive metal selected from thegroup consisting of gold, platinum, palladium, rhodium, ruthenium,iridium and alloys thereof.
 68. A medical device according to claim 65,wherein the oxide-resistant cladding comprises platinum.
 69. A medicaldevice according to claim 65, wherein the oxide-resistant claddingcomprises platinum iridium alloy.
 70. A medical device according toclaim 65, wherein the terminal conductor comprises an intermediate layerbetween the inner core and the oxide resistant cladding.
 71. A medicaldevice according to claim 70, wherein the oxide resistant claddingcomprises a noble metal or a noble metal alloy.
 72. A medical deviceaccording to claim 70, wherein the oxide resistant cladding comprises aconductive metal selected from the group consisting of gold, platinum,palladium, rhodium, ruthenium, iridium and alloys thereof.
 73. A medicaldevice according to claim 70, wherein the oxide-resistant claddingcomprises platinum.
 74. A medical device according to claim 70, whereinthe oxide-resistant cladding comprises platinum iridium alloy.
 75. Amedical device according to claim 70, wherein the intermediate layercomprises a refractory metal.
 76. A medical device according to claim70, wherein the intermediate layer comprises a film comprising titanium.77. A medical device according to claim 70, wherein the intermediatelayer comprises a film comprising niobium.
 78. A medical deviceaccording to claim 65, wherein the connection between the distal portionof the terminal conductor and the electrical device enclosed in thecontainer comprises a heat joined connection.
 79. A medical deviceaccording to claim 78, wherein the heat joined connection comprises aweld.
 80. A medical device according to claim 65, wherein the inner corecomprises tantalum or niobium, and wherein the oxide-resistant claddingcomprises a platinum or platinum-iridium alloy cladding.
 81. A medicaldevice according to claim 80, wherein the terminal conductor furthercomprises an intermediate layer between the inner core and the oxideresistant cladding.
 82. A medical device according to claim 81, whereinthe oxide resistant cladding comprises a noble metal or a noble metalalloy.
 83. A medical device according to claim 81, wherein the oxideresistant cladding comprises a conductive metal selected from the groupconsisting of gold, platinum, palladium, rhodium, ruthenium, iridium andalloys thereof.
 84. A medical device according to claim 81, wherein theoxide-resistant cladding comprises platinum.
 85. A medical deviceaccording to claim 81, wherein the oxide-resistant cladding comprisesplatinum iridium alloy.
 86. A medical device according to claim 81,wherein the intermediate layer comprises A refractory metal.
 87. Amedical device according to claim 81, wherein the intermediate layercomprises a film comprising titanium.
 88. A medical device according toclaim 81, wherein the intermediate layer comprises a film comprisingniobium.
 89. A feedthrough for use in an implantable medical device ofthe type having a hermetically-sealed container containing an electricaldevice, the feedthrough comprising: a generally annular ferrule adaptedto mate with an opening in the container; insulating material disposedwithin and coupled to the ferrule; and a terminal conductor extendingthrough the insulating material and having a proximal portion disposedoutside of the container and a distal portion disposed within thecontainer, the terminal conductor comprising an inner core and anoxide-resistant cladding on the inner core.
 90. The feedthrough of claim89, wherein the inner core comprises tantalum, a tantalum alloy,niobium, or a niobium alloy.
 91. The feedthrough of claim 90, whereinthe oxide-resistant cladding comprises platinum or platinum-iridium. 92.The feedthrough of claim 89, wherein the terminal conductor comprises anintermediate layer between the inner core and the oxide-resistantcladding.
 93. The feedthrough of claim 92, wherein the intermediatelayer comprises a refractory metal.
 94. The feedthrough of claim 92,wherein the intermediate layer comprises titanium.
 95. The feedthroughof claim 92, wherein the intermediate layer comprises niobium.
 96. Thefeedthrough of claim 89, further comprising a capacitive structuredisposed within a portion of the ferrule, the capacitive structure beingoperatively coupled to the terminal conductor.
 97. The feedthrough ofclaim 89, wherein the oxide resistant cladding is not located betweenthe capacitive structure and the inner core of the terminal conductor.98. The feedthrough of claim 89, wherein the oxide resistant cladding isnot located between at least a portion of the insulating material andthe inner core of the terminal conductor.
 99. The feedthrough of claim89, wherein the oxide resistant cladding comprises a conductive metalselected from the group consisting of gold, platinum, palladium,rhodium, ruthenium, iridium and alloys thereof.
 100. An implantablemedical device comprising: a hermetically-sealed container enclosing anelectrical device; a feedthrough coupled to the container, thefeedthrough comprising: a generally annular ferrule adapted to mate withan opening in the housing; insulating material disposed within andcoupled to the ferrule; and terminal conductor means for providing anelectrical pathway through the insulating material in the feedthrough,the terminal conductor means being joined to the electrical device inthe container by a connection formed through heat joining and includingan oxide-resistant coating, wherein the oxide resistant coating isselected from the group consisting of a cladding, a paint, a vacuumdeposited layer, a chemical vapor deposited layer, and a sputterdeposited layer.
 101. An implantable medical device for delivering atherapy, the device comprising: a hermetically-sealed containerenclosing an electrical device; a feedthrough coupled to the container,the feedthrough comprising: a generally annular ferrule adapted to matewith an opening in the container; insulating material disposed withinand coupled to the ferrule; and a terminal conductor extending throughand sealed to the insulating material and having a distal portiondisposed within the container, the terminal conductor comprising aninner core and an oxide-resistant coating on the inner core, wherein theoxide resistant coating is selected from the group consisting of acladding, a paint, a vacuum deposited layer, a chemical vapor depositedlayer, and a sputter deposited layer.
 102. A medical device according toclaim 101, wherein the oxide resistant coating comprises a noble metalor a noble metal alloy.
 103. A medical device according to claim 101,wherein the oxide resistant coating comprises a conductive metalselected from the group consisting of gold, platinum, palladium,rhodium, ruthenium, iridium and alloys thereof.
 104. A medical deviceaccording to claim 101, wherein the oxide-resistant coating comprisesplatinum.
 105. A medical device according to claim 101, wherein theoxide-resistant coating comprises platinum iridium alloy.
 106. A medicaldevice according to claim 101, wherein the terminal conductor comprisesan intermediate layer between the inner core and the oxide resistantcoating.
 107. A medical device according to claim 106, wherein the oxideresistant coating comprises a noble metal or a noble metal alloy.
 108. Amedical device according to claim 106, wherein the oxide resistantcoating comprises a conductive metal selected from the group consistingof gold, platinum, palladium, rhodium, ruthenium, iridium and alloysthereof.
 109. A medical device according to claim 106, wherein theoxide-resistant coating comprises platinum.
 110. A medical deviceaccording to claim 106, wherein the oxide-resistant coating comprisesplatinum iridium alloy.
 111. A medical device according to claim 106,wherein the intermediate layer comprises a refractory metal.
 112. Amedical device according to claim 106, wherein the intermediate layercomprises a film comprising titanium.
 113. A medical device according toclaim 106, wherein the intermediate layer comprises a film comprisingniobium.
 114. A medical device according to claim 101, wherein theconnection between the distal portion of the terminal conductor and theelectrical device enclosed in the container comprises a heat joinedconnection.
 115. A medical device according to claim 114, wherein theheat joined connection comprises a weld.
 116. A medical device accordingto claim 101 , wherein the inner core comprises tantalum or niobium, andwherein the oxide-resistant coating comprises a platinum orplatinum-iridium alloy cladding.
 117. A medical device according toclaim 116, wherein the terminal conductor further comprises anintermediate layer between the inner core and the oxide resistantcoating.
 118. A medical device according to claim 117, wherein the oxideresistant coating comprises a noble metal or a noble metal alloy.
 119. Amedical device according to claim 117, wherein the oxide resistantcoating comprises a conductive metal selected from the group consistingof gold, platinum, palladium, rhodium, ruthenium, iridium and alloysthereof.
 120. A medical device according to claim 117, wherein theoxide-resistant coating comprises platinum.
 121. A medical deviceaccording to claim 117, wherein the oxide-resistant coating comprisesplatinum iridium alloy.
 122. A medical device according to claim 117,wherein the intermediate layer comprises a refractory metal.
 123. Amedical device according to claim 117, wherein the intermediate layercomprises a film comprising titanium.
 124. A medical device according toclaim 117, wherein the intermediate layer comprises a film comprisingniobium.